1. Field of the Invention
The present invention relates to a method and devices for the implantation of artificial meshwork into the eye of a human or animal. The implant is performed on eyes with glaucoma so as to relieve the intraocular pressure in the diseased eye. More specifically, the present invention relates to devices used for implanting an artificial meshwork within an eye to lower the intraocular pressure while avoiding hypotony and a method of using the devices.
2. Description of the Related Art
Glaucoma is a disease of the eye that occurs most commonly in people over the age of fifty. Two million patients have been diagnosed with glaucoma. One million more have glaucoma but are not aware of it.
In glaucoma, the pressure within the eye increases and destroys the visual nerve fibers. A sharp anatomic angle exists at the junction between the iris and the inner surface of the cornea. At this angle, the fluids of the eye, which are called the aqueous humor, filter out of the anterior chamber of the eye and into the capillaries. In one type of glaucoma, the opening at the junction between the iris and the inner surface of the cornea where filtration occurs closes and aqueous humor builds up in the eye. Due to the excess of the aqueous humor in the eye, the pressure within the eyeball increases. If this increased pressure is sustained for long periods of time, then the optic nerve fibers can be permanently damaged and blindness will result.
For years, doctors have performed sclerotomy operations to relieve the intraocular pressure. The operations usually include a wide incision and a small opening is bored through the scleral tissue, which allows fluid to filter out and thereby lessen the pressure within the eyeball. Similar surgery can be performed less invasively with a laser.
When surgery is not an option, eye drops of a solution containing 0.25 to 5 percent of pilocarpine nitrate is dropped into the eye in the evenings and the mornings. This drug causes the pupil to contract, thus drawing the iris away from the cornea and opening the angle for filtration. This treatment may be continued for days or years. Another drug prescribed to patients is timolol maleate.
Both of these methods have complications.
The surgical process described above is generally not effective for more than five years. Postoperative complications associated with such surgical techniques, such as functional bleb failure due to scarring may occur. These scars are believed to be caused by the procedure's invasiveness and morbidity as well as a relatively long operation time. The usual surgery, generally known as trabeculectomy, lasts for more than half an hour.
Often patients still require glaucoma drugs. In complex cases, the patient is either submitted to a regimen involving daily subconjunctival injections of 5-FU for about two weeks or treated intraoperatively with topical applications of mitomycin C before opening the channel. This must be done in order to minimize the natural wound healing response which ultimately closes, by forming scars, the channel formed in surgery. Another problem is that the operation is less effective for patients with hyper-vascularization.
Approximately 37,000 eyes underwent surgeries involving incisions for glaucoma in 1987. The cost for each procedure is high, including postoperative care, in the first postoperative year alone. By the fifth postoperative year, about half of the eyes will require a second filtering operation. Further, the costs of glaucoma medications are quite expensive, and patient compliance with a doctor recommended regimen is quite low.
Some recently issued patents describe the use of tubes and tubes with valves to regulate the pressure in the anterior chamber of the eye. The surgery to perform these usually require removal of tissue in the eye and the tubes can become clogged as time passes. U.S. Pat. No. 4,936,825 teaches the use of a porous strand which is sewed and tied in the scleral tissue by using a needle. The pores in the string must run substantially the length of the strand. Since these pores are long and narrow, they may become easily blocked.